Landfill cover structure and design method thereof

Abstract

The present invention provides a landfill cover structure and a design method thereof. The landfill cover structure covers the surface of the landfill waste body and includes an exhaust layer adjacent to the landfill waste body and a compacted soil layer located above the exhaust layer. The exhaust layer is a mixture of recycled coarse aggregate and domestic waste incineration slag; the compacted soil layer includes a vegetation layer, a water storage layer, a drainage layer, and an impermeable layer from top to bottom. The design method is to first estimate the landfill gas flux F entering the landfill cover layer. LFG‑in The landfill cover layer design thickness L is calculated based on the estimated landfill gas flux in step S1. Construction is then performed based on the set thicknesses of the vegetation layer, water storage layer, drainage layer, impermeable layer, and exhaust layer. The landfill cover structure constructed from construction waste and municipal solid waste incineration slag in this invention not only solves the problem of waste disposal and the source of cover soil, but also realizes the resource utilization of slag and has environmental benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental geotechnical engineering, in particular to a landfill cover structure and a design method thereof. Background Art

[0002] In recent years, China's rapid urbanization has led to the demolition or renovation of numerous older buildings, resulting in a significant increase in the generation of construction waste. Despite the enormous volume of construction waste, its resource utilization rate remains low. At the same time, many of my country's sanitary landfills, built in the 1990s, are facing the need for subsequent closure and ecological restoration. If a single sanitary landfill's closure area is estimated at 100 hectares, over 500,000 cubic meters of greening soil will be required, indicating a significant demand for closure and cover materials. If construction waste could be used as landfill cover material, it would address both the waste disposal problem and the sourcing of cover soil, generating significant economic, social, and environmental benefits.

[0003] Methane is a greenhouse gas that exists in the atmosphere for a long time, and landfills are the third largest source of anthropogenic methane emissions. In order to alleviate the problem of global warming, it is very necessary to control landfill gas emissions, especially to reduce methane gas emissions. When the landfill gas production rate is high, the methane gas is recycled and reused. When the landfill gas production rate is extremely low, the methane can be oxidized through the landfill cover layer.

[0004] The cover layer is an important component of the landfill. As a barrier between the garbage pile and the atmospheric environment, it must play the role of anti-seepage and airtightness. The ecological soil cover layer is based on the water storage-release principle. It stores rainwater during rainfall and releases the stored water through soil evaporation and plant transpiration on sunny days, thereby reducing the leakage of the cover layer. It has safety, economic and ecological advantages and has been widely studied. However, the current research on the structure of the soil cover layer mainly focuses on the anti-seepage performance. How to meet both anti-seepage and landfill gas emission requirements deserves our attention. Summary of the Invention

[0005] The purpose of the present invention is to address the above-mentioned problems and provide a landfill cover layer structure and design method. The landfill cover layer structure constructed with construction waste and domestic waste incineration slag in the present invention is not only conducive to solving the problem of construction waste disposal and the source of cover layer soil, but also can realize the resource utilization of slag, and at the same time take into account the anti-seepage performance and safe emission of landfill gas, which has environmental benefits.

[0006] In order to achieve the above technical objectives, the present invention provides a landfill cover layer structure, which covers the surface of the landfill garbage body and includes an exhaust layer adjacent to the landfill garbage body and a compacted soil layer located above the exhaust layer. The exhaust layer is formed by mixing recycled coarse aggregate and domestic waste incineration slag in a mass ratio of 2 to 4:1 and then piling them up; the compacted soil layer includes, from top to bottom, a vegetation layer, a water storage layer, a drainage layer and an impermeable layer, wherein the water storage layer is formed by mixing recycled fine aggregate and domestic waste incineration slag in a mass ratio of 3 to 5:1 and then piling and compacting them; the drainage layer is formed by mixing recycled coarse aggregate and domestic waste incineration slag in a mass ratio of 2 to 4:1 and then piling and compacting them; the impermeable layer is made by adding recycled aggregate, cement and fly ash to recycled redundant soil, wherein the recycled aggregate content is 1%-15% of the recycled redundant soil, the cement content is 3%-18% of the recycled redundant soil, and the fly ash content is 1%-20% of the recycled redundant soil.

[0007] A preferred technical solution of the present invention is as follows: the vegetation layer is formed by a mixture of landfill soil, compost, recycled fine aggregate and domestic waste incineration slag, wherein the compost content is 5-15% of the landfill soil, the recycled fine aggregate content is 3-10% of the landfill soil, and the domestic waste incineration slag content is 3-10% of the landfill soil; the thickness of the vegetation layer is not less than 15 cm.

[0008] The preferred technical solution of the present invention is as follows: the thickness of the exhaust layer is 20 to 30 cm; the thickness of the water storage layer is not less than 50 cm; the thickness of the drainage layer is 20 to 40 cm; and the thickness of the anti-seepage layer is 40 to 80 cm.

[0009] The preferred technical solution of the present invention is as follows: the recycled aggregate is obtained by screening construction waste after soil removal and crushing using screening equipment, including recycled fine aggregate with a particle size of 2.00 to 4.75 mm and recycled coarse aggregate with a particle size greater than 4.75 mm; the recycled fine aggregate and recycled coarse aggregate are specifically obtained by stacking crushed construction waste on the first layer of screen surface, and the screen vibrates under the mechanical force of the machine, so that the construction waste in the screen rolls continuously in the horizontal and vertical directions, thereby obtaining coarse aggregate and fine aggregate of different particle sizes after screening through sieves of different sizes; the recycled redundant soil is the abandoned soil screened out during the soil removal process of construction waste, containing slag mixed with construction waste and crushed fine particles.

[0010] In order to achieve the above technical objectives, the present invention also provides a landfill cover structure design method, the method specifically comprises the following steps:

[0011] S1. First, estimate the landfill gas flux F entering the landfill cover LFG-in ;

[0012] S2. Calculate the design thickness L of the compacted layer in the landfill cover layer using the landfill gas flux estimated in step S1. The compacted soil layer includes, from top to bottom, a vegetation layer, a water storage layer, a drainage layer, and an impermeable layer. The thickness of the degassing layer in the landfill cover layer is determined to be 20 to 30 cm.

[0013] S3. Level and compact the landfill surface, construct the landfill cover layer step by step according to the landfill cover structure, and then test the thickness of the landfill cover structure based on the methane flux measured on the landfill cover surface.

[0014] A further technical solution of the present invention: The process of estimating the landfill gas flux entering the cover layer in step S1 is as follows:

[0015] ① Determine the thickness of each layer of garbage and the filling time based on the landfill operation records. Drill holes in the landfill to obtain garbage samples at different burial depths. Use the Fan's detergent fiber analysis method to measure the cellulose C and lignin L content of garbage samples at different depths, thereby calculating the C / L value of garbage samples at different burial depths. Then, calculate the landfill degradation index Y1 at different ages t according to the formula, and draw a relationship curve between the landfill degradation index Y1 and age t;

[0016] Y1=C / L(t) / C / L(t0)

[0017] Among them, C / L(t) is the C / L value of garbage at age t,

[0018] C / L(t0) is the C / L value of fresh garbage on the surface;

[0019] ② Combined with the relationship curve of landfill degradation index Y1 and age t, the landfill degradation index Y1 decreases rapidly during the short landfill time t1, which is the rapid degradation stage. The degradation rate slows down significantly during a considerable period of time from t1 to t2, which is the slow degradation stage. After t2, the degradation rate tends to be stable, which is the degradation stabilization stage. Therefore, the time t1 when the landfill is in the slow degradation stage is determined, and at this time t=t1;

[0020] ③ Calculate the gas production rate F of the entire landfill corresponding to time t1 according to the landfill gas production rate formula i , the landfill gas production rate formula is as follows:

[0021]

[0022] Among them, F i is the gas production rate of the i-th layer of garbage, kgLFG / m 2 / a;

[0023] ρ i is the density of the garbage in layer i, kg / m 3 ;h iis the thickness of the i-th layer of garbage, m;

[0024] L R0 , L S0 are the maximum gas production of rapidly degradable substances and slowly degradable substances in the landfill, m 3 / kg; k R 、k S are the gas production rate constants of rapidly degradable and slowly degradable substances in landfills, 1 / a; t i is the age of the garbage in the i-th layer, a; Pa is the atmospheric pressure; M LFG is the molar mass of landfill gas, kg / mol; R is the gas constant; T is the Kelvin temperature of the gas, K;

[0025] The time t1 is considered as the closure time. After that, the collected landfill gas is no longer economical and needs to be controlled by the oxidation capacity of the cover layer. At this time, the corresponding landfill gas production rate is the landfill gas flux F entering the cover layer. LFG-in .

[0026] A further technical solution of the present invention is that the calculation of the design thickness of the landfill cover layer in step S2 is to calculate the landfill gas flux F entering the landfill cover layer estimated in step S1. LFG-in The thickness L of the compacted soil in the cover layer is calculated based on Darcy's law. The formula of Darcy's law is as follows:

[0027]

[0028] In the above formula, k g is the gas permeability coefficient of the covering layer, m 2 ; μ is the viscosity of the gas, Pa·s;

[0029] P c is the safety control air pressure at the bottom of the cover layer, Pa; L is the thickness of the compacted soil in the cover layer, m.

[0030] A further technical solution of the present invention is as follows: in the step S3, methane flux is measured on the surface of the landfill cover layer to ensure that the landfill gas emissions meet the standard requirements. If the landfill gas methane is measured to exceed the emission standards, the compost dosage in the vegetation layer is increased to increase its organic matter content, thereby increasing the methane oxidation rate of the cover layer and increasing the methane consumption, or the closure time is extended to reduce the landfill gas flux entering the cover layer.

[0031] The preferred technical solution of the present invention is: the thickness L of the compacted soil layer in the covering layer is not less than 125 cm; the thickness of the vegetation layer in the compacted soil layer is not less than 15 cm, the thickness of the water storage layer is not less than 50 cm, the thickness of the drainage layer is 20 to 40 cm, and the thickness of the anti-seepage layer is 40 to 80 cm

[0032] Beneficial effects of the present invention: The landfill cover layer structure constructed with slag from the incineration of construction waste and domestic waste is not only conducive to solving the problem of the disposal of construction waste and the source of soil materials for the cover layer, but also realizes the resource utilization of slag, and has considerable economic benefits; the landfill cover layer structure takes into account both anti-seepage performance and safe landfill gas emissions, and has environmental benefits; the landfill cover layer structure design method is simple, easy to understand, and convenient to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of a landfill cover structure of the present invention;

[0034] Figure 2 It is a curve diagram showing the relationship between the landfill degradation index and the age in the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments. The accompanying drawings are drawings of the embodiments and are drawn in a simplified manner for the sole purpose of clearly and concisely illustrating the embodiments of the present invention. The technical solutions shown in the accompanying drawings are specific solutions of the embodiments of the present invention and are not intended to limit the scope of the invention claimed for protection. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] A landfill cover structure provided in the embodiment, such as Figure 1As shown, the landfill cover structure covers the surface of the landfill waste body and includes a degassing layer adjacent to the landfill waste body and a compacted soil layer located above the degassing layer. The degassing layer is formed by mixing recycled coarse aggregate and municipal solid waste incineration slag in a mass ratio of 2 to 4:1. The degassing layer is 20 to 30 cm thick. The compacted soil layer includes, from top to bottom, a vegetation layer, a water storage layer, a drainage layer, and an impermeable layer. The vegetation layer is formed by mixing landfill soil, compost, recycled fine aggregate, and municipal solid waste incineration slag. The compost content is 5-15% of the landfill soil, the recycled fine aggregate content is 3-10%, and the municipal solid waste incineration slag content is 3-10%. The vegetation layer is no less than 15 cm thick. The water storage layer is formed by mixing recycled fine aggregate and domestic waste incineration slag in a mass ratio of 3 to 5:1 and then stacking and compacting, and the thickness is not less than 50 cm; the drainage layer is formed by mixing recycled coarse aggregate and domestic waste incineration slag in a mass ratio of 2 to 4:1 and then stacking and compacting, and the thickness of the drainage layer is 20 to 40 cm; the anti-seepage layer is made by adding recycled aggregate, cement and fly ash to recycled redundant soil, wherein the recycled aggregate content is 1%-15% of the recycled redundant soil, the cement content is 3%-18% of the recycled redundant soil, and the fly ash content is 1%-20% of the recycled redundant soil, and the thickness of the anti-seepage layer is 40 to 80 cm.

[0037] The recycled aggregate described in the embodiment is the aggregate obtained by screening the construction waste after soil removal and crushing using screening equipment, including recycled fine aggregate with a particle size of 2.00 to 4.75 mm and recycled coarse aggregate with a particle size greater than 4.75 mm; the recycled fine aggregate and recycled coarse aggregate are specifically obtained by piling the crushed construction waste on the first layer of screen surface, and the screen vibrates under the mechanical force of the machine, causing the construction waste in the screen to roll continuously in the horizontal and vertical directions, thereby obtaining coarse aggregate and fine aggregate of different particle sizes after screening through sieves of different sizes; the recycled redundant soil is the abandoned soil screened out during the soil removal process of the construction waste, containing slag mixed with the construction waste and fine particles after crushing.

[0038] Example: Taking a municipal solid waste landfill as an example, the landfill cover structure includes a compacted soil layer and a gas exhaust layer. The compacted soil layer includes a vegetation layer, a water storage layer, a drainage layer, and an impermeable layer. First, the landfill gas flux entering the landfill cover is estimated, and the required thickness of the landfill cover is calculated. Then, the landfill cover structure is checked based on the methane flux measured on the surface of the landfill cover.

[0039] In this embodiment, the vegetation layer is composed of a mixture of landfill soil, compost, recycled fine aggregate, and domestic waste incineration slag, with the compost content being 5-15% of the landfill soil, the recycled fine aggregate being 3-10%, and the domestic waste incineration slag being 3-10%. The thickness should be no less than 15 cm. The water storage layer is composed of a mixture of recycled fine aggregate and domestic waste incineration slag in a mixing ratio of 3 to 5:1, with a thickness of no less than 50 cm. The drainage layer is composed of recycled coarse aggregate and domestic waste incineration slag. The mixture is made of recycled redundant soil in a ratio of 2 to 4:1 and a thickness of 20 to 40 cm. The anti-seepage layer is made by adding recycled aggregate, cement, fly ash and other curing agents to the recycled redundant soil. The recycled aggregate content is 1%-15% of the recycled redundant soil, the cement content is 3%-18% of the recycled redundant soil, and the fly ash content is 1%-20% of the recycled redundant soil. The thickness is 40 to 80 cm. The exhaust layer is made of recycled coarse aggregate and domestic waste incineration slag in a ratio of 2 to 4:1 and a thickness of 20 to 30 cm.

[0040] The estimation process of the landfill gas flux entering the cover layer in this embodiment is as follows:

[0041] ① According to the landfill operation records, the thickness of each layer of garbage landfill and the filling time are determined. Drill holes in the landfill to obtain garbage samples of different burial depths. The cellulose C and lignin L content of the garbage samples are measured according to the Fan's detergent fiber analysis method. The C / L values ​​of garbage samples of different burial depths are calculated, and the relationship curve between the landfill degradation index Y1=C / L(t) / C / L(t0) and the corresponding age t can be obtained, as shown in the figure below: Figure 2 As shown, C / L(t) is the C / L value of garbage at age t, and C / L(t0) is the C / L value of fresh garbage on the surface. It can be seen from the figure that when the age t = t1 = 2 years, the landfill garbage begins to degrade slowly.

[0042] ② According to the landfill gas production rate formula Calculate the gas production rate of the entire landfill corresponding to time t1. The values ​​of the parameters in the formula are determined according to the analysis of the garbage composition of the landfill and the gas extraction test. The calculation assumes that the garbage of the same composition is landfilled each time, ρ i =900kg / m 3 , h i =8m,k R =1.825a -1 , k S =0.2555a -1 , L R0 =103.8m 3 / t,L S0 =34.4m 3 / t, Pa = 101.325 kPa, M LFG=0.03kg / mol, R=8.314J / (mol·K), T=293.15K.

[0043] When the age t is 2 years, it can be considered as the closure time. At this time, the corresponding landfill gas production rate is the landfill gas flux F entering the cover layer. LFG-in =241.64kgLFG / m 2 / a.

[0044] The required thickness of the landfill cover in this embodiment is calculated by inversely deducing the compacted soil thickness L based on Darcy's law:

[0045]

[0046] The values ​​of the parameters in the formula are determined according to the test, k g =1.4×10 -13 m 2 , μ=1.35×10 -5 Pa·s,P c =750Pa, and the thickness of the compacted soil in the cover layer is calculated to be L = 126.60cm, which meets the requirements for the thickness of each layer in the landfill cover structure described in the present invention, that is, the thickness should be no less than 125cm. The thickness of the compacted soil can be determined to be 125cm, and then the thickness of each layer can be determined based on the thickness requirements of each layer in the compacted soil layer.

[0047] After the thickness of the cover layer is determined, the landfill surface is leveled and compacted, and the landfill cover layer structure of the present invention is gradually constructed in layers.

[0048] In this embodiment, methane flux is measured on the surface of the landfill cover layer to ensure that landfill gas emissions meet standard requirements. If the measured landfill gas methane exceeds the emission standard, measures such as increasing the amount of compost in the vegetation layer to increase its organic matter content and thereby increase the methane oxidation rate of the cover layer and increase methane consumption can be taken, or the closure time can be extended to reduce the landfill gas flux entering the cover layer.

[0049] The above describes the embodiments of the present invention in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned implementation methods. Under the guidance of the present invention, technical personnel in the same field can make modifications, replacements and improvements within the principles and purpose of the present invention, which are all included in the scope of protection of the present invention.

Claims

1. A method for designing a landfill cover structure, characterized in that: The specific steps are as follows: S1. First estimate the landfill gas flux into the landfill cover ; S2. Calculate the compacted soil thickness L in the landfill cover layer using the estimated landfill gas flux in step S1; and determine the thickness of the exhaust layer in the landfill cover layer to be 20-30 cm; the designed landfill cover layer thickness is the landfill gas flux estimated in step S1 into the landfill cover layer. The thickness L of the compacted soil in the cover layer is calculated based on Darcy's law. The formula of Darcy's law is as follows: ， In the above formula, is the gas permeability coefficient of the covering layer, m 2 ; is the viscosity of the gas, ; To safely control the air pressure at the bottom of the covering layer, ; L is the thickness of compacted soil in the cover layer, m; S3. Level and compact the landfill surface, construct the cover layer in layers according to the landfill cover structure, and then verify the thickness of the landfill cover structure based on the methane flux measured on the landfill cover surface; The landfill cover structure covers the surface of the landfill garbage body, including an exhaust layer adjacent to the landfill garbage body and a compacted soil layer located above the exhaust layer, wherein the exhaust layer is formed by mixing recycled coarse aggregate and domestic waste incineration slag in a mass ratio of 2 to 4:1 and then stacking; the compacted soil layer includes a vegetation layer, a water storage layer, a drainage layer and an anti-seepage layer from top to bottom, wherein the water storage layer is formed by mixing recycled fine aggregate and domestic waste incineration slag in a mass ratio of 3 to 5:1 and then stacking and compacting; the drainage layer is formed by mixing recycled coarse aggregate and domestic waste incineration slag in a mass ratio of 2 to 4:1 and then stacking and compacting; the anti-seepage layer is made by adding recycled aggregate, cement and fly ash to recycled redundant soil, wherein the recycled aggregate content is 1%-15% of the recycled redundant soil, the cement content is 3%-18% of the recycled redundant soil, and the fly ash content is 1%-20% of the recycled redundant soil.

2. The method for designing a landfill cover structure according to claim 1, characterized in that: The vegetation layer is composed of a mixture of landfill soil, compost, recycled fine aggregate and domestic waste incineration slag, wherein the compost content is 5-15% of the landfill soil, the recycled fine aggregate content is 3-10% of the landfill soil, and the domestic waste incineration slag content is 3-10% of the landfill soil. The thickness of the vegetation layer is not less than 15 cm.

3. The method for designing a landfill cover structure according to claim 1 or 2, characterized in that: The thickness of the exhaust layer is 20-30 cm; the thickness of the water storage layer is not less than 50 cm; the thickness of the drainage layer is 20-40 cm; and the thickness of the anti-seepage layer is 40-80 cm.

4. The method for designing a landfill cover structure according to claim 1 or 2, characterized in that: The recycled aggregate is obtained by removing soil from construction waste, crushing it, and then screening it with screening equipment, including recycled fine aggregate with a particle size of 2.00 to 4.75 mm and recycled coarse aggregate with a particle size greater than 4.75 mm; the recycled fine aggregate and recycled coarse aggregate are specifically obtained by piling the crushed construction waste on the first layer of screen surface, and the screen vibrates under the mechanical force of the machine, causing the construction waste in the screen to roll continuously in the horizontal and vertical directions, thereby obtaining coarse aggregate and fine aggregate of different particle sizes after screening through sieves of different sizes; the recycled redundant soil is the abandoned soil screened out during the soil removal process of construction waste, containing slag mixed with construction waste and crushed fine particles.

5. The method for designing a landfill cover structure according to claim 1, characterized in that: The estimation process of the landfill gas flux into the cover layer in step S1 of the design method is: ① According to the landfill operation records, the thickness of each layer of garbage landfill and the filling time are determined. Drill holes in the landfill to obtain garbage samples of different burial depths. The cellulose C and lignin L contents of garbage samples of different depths are measured by Fan's detergent fiber analysis method, and the cellulose C and lignin L contents of garbage samples of different burial depths are calculated. The landfill degradation index Y1 at different ages t is calculated according to the formula, and a relationship curve between the landfill degradation index Y1 and age t is drawn; in, It is garbage of age t value, It's fresh garbage on the surface value; ② By observing the relationship curve between the landfill degradation index Y1 and the age t, it is determined that the period from 0 to t1 is the rapid degradation stage. After the landfill time t1, the landfill degradation index Y1 decreases slowly and reaches a stable stage, thus determining that the time when the landfill is in the slow degradation stage is t1, at which time t=t1; ③ Calculate the gas production rate of the entire landfill corresponding to time t1 according to the landfill gas production rate formula , the landfill gas production rate formula is as follows: ， in, is the gas production rate of the i-th layer of garbage, ; is the density of garbage in layer i, ; is the thickness of the i-th layer of garbage, m; 、 are the maximum gas production of rapidly degradable substances and slowly degradable substances in landfills, ; 、 are the gas production rate constants of rapidly degradable and slowly degradable substances in landfills, ; is the age of the garbage in layer i, ; is the atmospheric pressure; is the molar mass of landfill gas, ; is the gas constant; T is the Kelvin temperature of the gas, K; The time t1 is considered as the closure time. After that, the collected landfill gas is no longer economical and needs to be controlled by the oxidation capacity of the cover layer. At this time, the corresponding landfill gas production rate is the landfill gas flux entering the cover layer. .

6. The method for designing a landfill cover structure according to claim 1, characterized in that: In step S3 of the method for designing the landfill cover structure, methane flux is measured on the surface of the landfill cover to ensure that landfill gas emissions meet standard requirements. If the landfill gas methane is measured to exceed the emission standard, measures are taken to increase the amount of compost in the vegetation layer to increase its organic matter content, thereby increasing the methane oxidation rate of the cover layer and increasing methane consumption, or to extend the closure time to reduce the landfill gas flux entering the cover layer.

7. The method for designing a landfill cover structure according to claim 1, characterized in that: The thickness L of the compacted soil in the covering layer is not less than 125 cm; the thickness of the vegetation layer in the compacted soil layer is not less than 15 cm, the thickness of the water storage layer is not less than 50 cm, the thickness of the drainage layer is 20~40 cm, and the thickness of the anti-seepage layer is 40~80 cm.

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